.Net messaging pub/sub pattern

So I have an .Net application that is running on NancyFx (needs to be platform agnostic). I have a requirement that I need to send a notification when a certain event happens (subscription). The notification will implement this interface:

public interface INotification
{
    public void Notify();
}

There will be many different implementations for this e.g. Email, Pushbullet, Pushover etc.

What I am struggling with is how to actually implement this so that all implementations of INotification will execute Notify() when there is a subscription.

Can anyone point me in the right direction.

I don't really want to use any sort of external queues, since the application will be running on the users machines.